O trato retino-hipotalâmico no mocó (Kerodon rupestris): Um estudo de traçado anterógrado com a subunidade b da toxina colérica

The light, besides the vision stimuli, controls other process completely independent of image formation, such as the synchronization of the organismic circadian rhythms to the enviromental light/dark cycle. In mammals, this adjust occurs through the retinohypothalamic tract, a direct retinal projection to the suprachiasmatic nucleus, considered to be the major circadian pacemaker. Early studies have identified only the suprachiasmatic nucleus as a retinal target in the hypothalamus. However, using more sensitive neuroanatomic tracers, other retinorecipient hypothalamic regions outside to suprachiasmatic nucleus were pointed in a great number of mammalian species. In this study, the retinohypothalamic tract was shown in the rock cavy (Kerodon rupestris), an endemic rodent of the semiarid region of the Brazilian Northeast, using unilateral intravitreal injections of cholera toxin subunit b as a neuronal tracer. The results reveal that in the rock cavy, besides the suprachiasmatic nucleus, several hypothalamic regions receive direct retinal projection, such as the ventrolateral preoptic nucleus, medial and lateral preoptic areas, the supraoptic nucleus and bordering areas, anterior, lateral and rectrochiasmatic hypothalamic areas, and the subparaventricular zone. The results are discussed by comparing with those of the literature, into a functional context

Projeção retiniana, caracterização citoarquitetônica e neuroquímica da zona incerta do moco (Kerodon rupestris)

The Zona Incerta (ZI) is embryologically derived from the ventral thalamus, in continuity with the reticular nucleus of the thalamus. Studies usingneural tracers technics have allowed identify a complex connectional map including the ZI. Futhermore, cytochemical, molecular and functional data have shown abundant variability in the neurochemical contend in the ZI, as well as,the involvement of the ZI in the modulation of nociception, attention, alertness, control and maintenance of posture and control of visceral activity. This work aims to characterize the cytoarchitecture, neurochemical content of the ZI in the rock cavy (Kerodon rupestris), and a direct retinal-ZI pathway present in this species. The Nissl staining is effective for the delineation and characterization of ZI citoarchitecture. ZIc receives a contralateral retinal projection showing varicosities, suggesting a modulatory character of photic information. The ZI in the rock cavy, as in others rodents and primates, is characterized by a complex neurochemical signature. The ZI neurochemistry presents great diversity, especially in the medial portion of ZIr, where we have found immunoreactivity of all neuroactive substances investigated, and that NOS-IR, GFAP and CR helped the delimitation of middle ZI in ZId and ZIv. Nevertheless, just 5-HT-IR fibers are present in all subdivisions of the ZI. These data demonstrate the great wealth of the neurochemistry of rock cavy s ZI and a direct retinal modulation in the ZI, helping to explain it s broad functional repertory